This invention relates to pitch for use in the manufacture of high-performance carbon fibers and a process for the production of said pitch. More particularly, the invention relates to mesophase pitch of a type that is produced by polymerizing condensed polycyclic aromatic hydrocarbons or substances containing them in the presence of HF/BF.sub.3 and which is reduced in the tendency to smoke during the spinning.
Processes for producing mesophase pitch by polymerizing condensed polycyclic aromatic hydrocarbons or substances containing them in the presence HF/BF.sub.3 are described in U.S. Pat. No. 4,789,455 and U.S. Pat. No. 4,891,126. U.S. Pat. No. 4,891,126 also teaches mesophase pitch that is produced by polymerizing naphthalene, anthracene, phenanthrene, pyrene and other skeleton containing condensed polycyclic hydrocarbons in the presence of HF/BF.sub.3. U.S. Pat. No. 5,182,010 discloses mesophase pitch that is produced by polymerizing naphthalene derivatives such as methylnaphthalene that have at least one methyl group. The mesophase pitch of the kinds described in these prior patents is drawing increasing attention as a precursor of inexpensive carbon artifacts since it does not require complicated steps in polymerization.
The mesophase pitch is also used as a precursor of high-performance carbon fibers and in this case it is important that the pitch (1) be homogeneous in the absence of gels and (2) contain the least amounts of light substances which will either foul spinning nozzles due to smoking during spinning or cause structural defects. To meet these requirements, light components are distilled off the pitch. Since the light components to be removed have boiling points of about 500.degree.-700.degree. C. at atmospheric pressure, the operation of their removal must inevitably be performed under high-temperature conditions. As a result, a pyrolytic reaction occurs to cause an unwanted reaction for the generation of light components, making it difficult to achieve complete removal of the light components from the pitch; additionally, a reaction for conversion to heavy substances also occurs due to thermal polymerization and not only are formed by product gels but also the softening point of the pitch will increase abnormally, presenting considerable difficulty in using it as a precursor of high-performance carbon fibers.